For some time there has been interest in harvesting energy from vibrations or motion such as walking to provide power as a replacement for batteries. Two sources of electric power have been used previously piezoelectric devices and magnetic devices.
U.S. Pat. Nos. 4,412,355 and 4,471,353 disclose a switch that powers a transmitter to switch on a remote light using the current generated by a magnet on a vibrating reed interacting with a coil.
U.S. Pat. No. 5,818,132 generates electric power from the linear movement of a magnet through a coil
U.S. Pat. No. 5,838,138 uses a sprung magnet on a key of a key board moving in a coil to generate electric power to recharge batteries on a portable computer or similar device.
U.S. Pat. No. 5,844,516 discloses a wireless remote controller, which replaces batteries with a piezo generator actuated by a push button or turning wheel.
U.S. Pat. No. 5,945,749 discloses a power generator for devices on a train which uses the motion of the train to oscillate a magnetic piston within a coil.
U.S. Pat. No. 6,220,719 provides a torch with a magnet able to reciprocate within the torch barrel which is wound with coils. The arrangement includes a capacitor for storing charge.
U.S. Pat. No. 6,291,901 discloses an automobile wheel with a magnet and coil arranged so that deflection of the tire causes relative motion between the magnet and the coil to generate electricity.
WO 01/20760 discloses a micro piezo generator comprising a micro fabricated silicon cantilever with a piezo layer on the cantilever so that vibration of the cantilever to generate current.
There is a need for a device which can generate electrical power without being actively actuated but which simply relies on the vibration or movement of the body or article to which it is attached.